Sources of Organic and Inorganic Halogens to the Polar and Temperate Marine Boundary Layer Marvin Shaw Doctor of Philosophy University of York Chemistry August 2011 Abstract Very short lived halogenated substances (VSLH) are of importance for the transport of reactive halogens to the troposphere and lower stratosphere, whereas molecular halogens are of specific importance to the Marine Boundary Layer (MBL). This thesis describes the field deployment of a ground based gas chromatography mass spectrometry (GC/MS) in the Canadian sub-Arctic for the determination of VSLH in seawater/sea-ice and air with a view to identify dominant sources to the MBL in the region. MBL mixing ratios of VSLH were determined from a surface site (55.28°N, 77.77°W) on the south east of Hudson Bay,(Kuujjuarapik, Canada) during the 19th -27th of February. Elevated mixing ratios of the Volatile Organic Iodine Compounds (VOIC) coincided with airmasses reaching the ground site that had previously transected regions of open water in the Bay (between 10 – 200 km away), suggesting leads/polynyas are the dominant source of VOIC within the region. This observation is supported by laboratory experiments conducted with artificial sea ice in a cold chamber (School of Earth and Environment, Leeds University) in which physico- chemical properties of the hypersaline brine, sea-ice and the underlying seawater were measured to quantify the vertical transport of a comprehensive range of volatile organic iodinated compounds (VOICs) at air temperatures of -3 and -14 oC. The results suggest that VOIC gas transfer velocities from diffusion through the sea-ice alone are at least 60 times lower at -3 ºC than gas exchange from leads and polynas during the winter (assuming a sea- ice fractional coverage of 0.1). This has significant implications for in situ VOIC losses within the brine from chlorination, hydrolysis and photolysis processes and it is unlikely that measurable concentrations of VOICs would survive vertical transport from the underlying seawater to the surface sea ice quasi-liquid layer. Further laboratory work within this thesis suggests that gaseous I2 evolution from the oxidation of iodide in the world’s oceans by atmospheric ozone is a viable source of iodine to the MBL, but its strongly constrained by the iodide and dissolved organic carbon (DOC) content of the surface ocean. i Contents List of Figures viii List of Tables xv 1. Introduction to Atmospheric Halogen Sources and Chemistry 1 1.1 Tropospheric Oxidative Chemistry 2 1.2 Impacts of Tropospheric Halogen Chemistry 6 1.2.1 Gas phase halogen chemistry 8 1.2.2 Halogen NOX chemistry 11 1.3 Sources of Halogens to the Atmosphere 12 1.3.1 Sea-ice and sea salt aerosol halogenated source gas emissions 12 1.3.2 Organo halogen emissions 13 1.3.2.1 Biogenic halogenated source gas emissions 14 1.3.2.2 Abiotic halogenated source gas emissions 16 1.3.3 Terrestrial halogenated source gas emissions 16 1.4 Thesis Layout 18 ii 2. Experimental 19 2.1 Analyte pre-concentration and injection 20 2.2 Purge and trap 22 2.3 Gas Chromatography 23 2.3.1 Fundamentals of Chromatographic Separation 24 2.3.2 The Plate Theory of Chromatography 25 2.3.3 The Rate Theory of Chromatography 26 2.4 Mass Spectrometry 30 2.4.1 The Ion Source 31 2.4.2 The Mass Analyser 32 2.4.3 Detectors 36 2.5 GC/MS Experimental Set-up 37 2.6 Normalization and Calibration of Instruments 43 2.6.1 Preparation of halocarbon gas standard 43 2.6.2 National Physics Laboratory standard 44 2.6.3 Deuterated halocarbon gas standard 44 2.6.4 Permeation oven calibration 44 2.6.5 Perm oven valve optimization 47 2.6.6 Permeation tube degradation study 50 2.6.7 Propagation of errors for calibration 52 2.6.8 COBRA campaign data normalization 54 2.6.9 Laboratory cold chamber data normalization 56 2.7 UV-Visible spectrophotometry 60 2.7.1 Principles of UV-Vis spectrophotometry 60 2.7.2 Solution preparation 64 2.7.3 Preparation of 0.01 M phosphate buffer solution 65 2.7.4 Preparation of iodine solutions 65 2.7.5 Preparation of dissolved organic carbon extract 65 2.7.6 Quantitative determination of the dissolved organic extract 66 2.7.7 Quantitative determination of Chlorophyll a 67 iii 3. Evidence for the abiotic production and direct emission of iodine from surface seawater in the presence of gaseous ozone 68 3.1 Introduction 69 3.1.1 Abiotic molecular iodine evolution from seawater 69 3.1.2 Measurement techniques previously used for gaseous I2 determination 73 3.2 Development and optimization of a hexane solvent trap and spectrophotometric methods for the determination of gaseous I2 74 3.2.1 Generation of a molecular iodine test source 75 3.2.2 Optimization of a spectrophotometric method for I2 detection 75 3.2.3 Molecular iodine derivatisation using leucocrystal violet 76 3.2.4 Optimisation of solvent trap for gaseous I2 enrichment 78 3.2.5 Iodine losses due to interactions with ozone in hexane 87 3.3 Experiments of iodide oxidation using ozone 92 3.3.1 Experimental set-up 92 3.3.2 Ozone deposition control experiments 94 3.3.3 Iodine emission control experiments 95 3.4 Enhanced ozone uptake by seawater and iodide solutions 95 3.5 Comparison of observed ozone uptake coefficients to theoretical estimates 104 3.6 Molecular iodine evolution from salt solutions via the I + O3 interaction 107 3.6.1 Molecular iodine losses attributed to wall loss 107 3.6.2 Molar balance of iodine species in experimental system 109 3.6.3 Evolution of I2 from aqueous iodide in the presence of gaseous ozone 110 3.6.4 Rate of I2 evolution as a function of [O3] and [I ] 111 3.7 Study of the effect of DOC concentrations on O3 deposition and I2 evolution 116 3.7.1 The effect of aqueous DOM on ozone reactivity at the sea surface 117 3.7.2 Evolution of gaseous I2 in the presence of aqueous DOM concentrations 119 3.8 Conclusions 125 iv 4. Evidence for the emission of reactive halocarbons from open leads in sub-Arctic sea ice during the COBRA campaign 126 4.1 Introduction 127 4.1.1 Tropospheric polar halogen chemistry 127 4.1.2 Impacts of ODEs on Arctic chemistry 128 4.1.3 Halogen sources to the polar boundary layer 130 4.1.3.1 Saline sea-ice, snowpack and sea salt aerosol as a direct halogen source 130 4.1.3.2 Frost flowers and derived aerosols as a source of reactive halogens 130 4.1.4 Sources of VSLH 133 4.1.5 The COBRA Campaign 135 4.2 Experimental 137 4.2.1 Site and Sampling Details 137 4.2.2 Online air VSLH measurements 139 4.2.3 Online air measurements calibration and normalization 140 4.2.4 Air mass classification using calculated back trajectories 142 4.3 Results 144 4.3.1 Meteorological conditions during COBRA campaign 144 4.3.2 Ambient air determinations of poly-brominated organics 147 4.3.3 Ambient air determinations of mono-iodinated and poly-halogenated organics 149 4.3.4 Determination of air mass histories 153 4.3.5 Statistical analysis 158 4.3.6 Influence of leads/polynyas in sea ice on atmospheric surface temperature 160 4.3.7 Oceanography of leads and polynas in sea ice 161 4.3.8 Observed effects of brominated organics on surface ozone 163 4.3.9 Observed effects of VOICs on MBL composition 166 4.4 Conclusions 170 v 5. Gas diffusion through columnar sea ice: Implications for halocarbon fluxes in the seasonal sea ice zone 173 5.1 Introduction 174 5.1.1 Sea ice formation 174 5.1.2 Sea ice dynamics 175 5.1.3 Nutrient exchange through sea ice 175 5.1.4 Biogeochemistry of sea ice 176 5.1.5 Sea ice radiative transfer and its effect on the photic zone 177 5.2 Experimental 178 5.2.1 Experimental chamber 178 5.2.2 Experimental procedure 180 5.2.3 Aqueous VOIC in-situ losses 184 5.2.4 Aqueous under-ice VOIC sampling 185 5.2.5 Artificial ice and brine VOIC sampling 186 5.2.6 Internal standardization and external calibration 187 5.2.7 VOIC fluxes calculated from a consideration of the molar balance 187 5.2.8 Calculation of VOIC fluxes from the QLL to air 188 5.2.9 Calculation of VOIC gas transfer velocities 190 5.2.10 Calculation of mass diffusion lengths 191 5.2.11 Sea water and sea ice sampling during the COBRA campaign 191 5.3 Results and Discussion 194 5.3.1 Temperature distributions in Leeds chamber artificial sea ice 194 5.3.2 Distribution of salinity in sea ice 197 5.3.3 Evolution of artifical seawater salinity 204 5.3.4 Calculated VOIC diffusion coefficients and brine volumes through sea-ice 206 5.3.5 Depth resolved VOIC concentrations within sea ice 208 5.3.6 Depth resolved VOIC concentrations in fresh ice 215 5.3.7 Under-sea ice VOIC concentration evolution 217 5.3.8 Calculated diffusive fluxes from the QLL to air 219 5.3.9 Comparison of sea-ice-air to sea-air fluxes 220 vi 5.4 Physico-chemical characteristics of Hudson Bay sea ice 223 5.4.1 Salinity distribution through Hudson Bay Sea ice 223 5.4.2 Nutrient exchange through Hudson Bay sea ice 226 5.4.3 Chlorophyll a distributions within Hudson Bay 227 5.4.4 Biogenic VOIC production 230 5.4.5 Abiotic production of halogenated organic compounds 231 5.4.6 VOIC and VOBC lifetimes in Hudson Bay sea ice 232 5.4.7 Distribution of halogenated organics through Hudson Bay sea ice 235 5.4.8 Comparison of sea-ice-air to sea-air fluxes within Hudson Bay 243 5.5 Discussion 245 5.5.1 Advantages and limitations of ice tank experiments 246 5.5.2 Conclusions 246 Appendix 248 Glossary 264 References 266 vii List of Figures 1.1 A simplified schematic representation of the proposed “bromine explosion” mechanism 6 1.2 Simplified mechanism of reactive halogen cycling in the MBL 13 2.1 Diagram showing valve position and flow channel during online sampling, in